This invention relates to a vacuum-type circuit interrupter having contacts primarily of beryllium and, more particularly, relates to an interrupter of this type that has improved shielding means for preventing the formation of a damaging arc spot on the flexible metallic bellows of the interrupter during high current interruptions.
The usual vacuum interrupter comprises a flexible metal bellows disposed around the movable contact rod of the interrupter and providing a flexible seal around the rod that allows axial motion of the rod. Typically, this bellows extends into the envelope of the interrupter, and a guide is disposed within the bellows to guide the movable contact rod during its axial motion. The metal bellows typically has a thin wall exposed to the vacuum within the envelope, and it is most important that no arc spot be allowed to form on the exposed surface of this wall since such an arc spot can quickly burn a hole through the thin wall.
In conventional vacuum interrupters having copper-base contacts, this has not been a serious problem even during high current interruptions. There seems to be little tendency in such interrupters for arc spots to develop on the bellows, assuming a conventional shield is provided for the bellows. But with interrupters having contacts of beryllium, I have observed a much greater tendency for arc spots to form on the bellows. This may be due to the greater mobility of the arc-generated beryllium vapor as compared to that of copper.